refactor(filters): share the attenuation interlock between fil_trans and fil_comb

The DMM-through / CCM-active check now lives in _attenuation_allowed and
fil_trans calls it, so there is one copy rather than two drifting ones.
A guard that is duplicated is a guard that gets fixed in one place only.

Behaviour is unchanged: the same three PVs are read with the same
fallbacks, the same warning is printed, the same default-NO prompt is
raised through OMNYTools.yesno, the same "Safe fallback" of refusing
when no prompt is available applies, and fil_trans(1) still bypasses the
check entirely.

Split from the previous commit so that this half can be reverted on its
own if it misbehaves at the beamline, without taking fil_comb with it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017kLGTqTyXzTT4swt3CfTkV

csaxs_bec/bec_ipython_client/plugins/cSAXS/filter_transmission.py

@@ -203,45 +203,9 @@ class cSAXSFilterTransmission:
         # Only allow fil_trans < 1 when DMM is in THROUGH (both)
         # and CCM energy > 1 keV. fil_trans(1) is always allowed.
         # -------------------------------------------------------
-        if transmission < 1.0:
-            try:
-                dmm_trans = float(epics_get("X12SA-OP-DMM-EMLS-3010:THRU"))
-            except Exception:
-                dmm_trans = -1
-            try:
-                dmm_rot = float(epics_get("X12SA-OP-DMM-EMLS-3030:THRU"))
-            except Exception:
-                dmm_rot = -1
-            try:
-                ccm_energy = float(epics_get("X12SA-OP-CCM1:ENERGY-GET"))
-            except Exception:
-                ccm_energy = -1
-
-            allowed = (dmm_trans == 1) and (dmm_rot == 1) and (ccm_energy > 1)
-
-            if not allowed:
-                print("\n⚠️  SAFETY WARNING: Reducing transmission (< 1) typically requires:")
-                print("   - DMM translation in THROUGH (THRU == 1)")
-                print("   - DMM rotation in THROUGH (THRU == 1)")
-                print("   - CCM energy > 1 keV")
-                print("\nCurrent state:")
-                print(f"   DMM translation THRU : {dmm_trans}")
-                print(f"   DMM rotation THRU    : {dmm_rot}")
-                print(f"   CCM energy (keV)     : {ccm_energy}")
-
-                # Ask user (default = NO)
-                if hasattr(self, "OMNYTools") and hasattr(self.OMNYTools, "yesno"):
-                    proceed = self.OMNYTools.yesno(
-                        "Conditions not satisfied. Proceed anyway?",
-                        default="n",
-                    )
-                else:
-                    # Safe fallback
-                    proceed = False
-
-                if not proceed:
-                    print("Aborted. Transmission unchanged.")
-                    return None
+        if transmission < 1.0 and not self._attenuation_allowed():
+            print("Aborted. Transmission unchanged.")
+            return None
         
         # --- Energy handling (EPICS only) ---
         if energy_kev is None: